1. Field of the Invention
This invention relates to optical scanners and particularly to scanners for scanning a coherent beam of radiation for electrophotographic copiers and printers.
2. Description of the Related Art
Optical scanners utilizing a polygonal mirror body rotated about an axis are widely used. Such scanners have several drawbacks. Very slight differences in the angular positioning or planarity of the faces of the polygon can cause the scanned beam to "wobble", which results in a variation in the placement of the beam on the object surface. This can relate in unreliable data transmission. Further, each such polygon has its own "signature" and it is difficult to obtain polygonal scanners having a high degree of uniformity. Moreover, the drive systems for the scanners are subject to wear, which imparts additional wobble and other inconsistencies over the life of the scanner unit. Also, these scanners are unidirectional in the sense that the scanned beam is only moved in the direction of rotation of the polygonal mirror. In addition, the scan characteristics of the polygonal type scanner are limited by the mechanical parameters of the scanners, such as the size and number of the mirror faces and the drive speed range of the scanner motor. Further, such units are somewhat large and have significant space requirements. In addition, units with acceptable levels of precision are expensive.
Galvanometer scanners are also used for scanning optical beams. Such scanners rotate a reflected surface back and forth in an arc to scan an incident beam. These scanners have limited scan deflection capabilities.